In this program you can calculate the area of a circle by its radius.
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import java.io.*; import java.util.Scanner; import java.text.*; class Testprogram { public static void main(String [] args) { double eingabe1, ergebnis; DecimalFormat f = new DecimalFormat("#0"); DecimalFormat g = new DecimalFormat("#0.00"); System.out.println("Please enter the radius of the circle in cm!"); Scanner eingabe = new Scanner(System.in); eingabe1 = Integer.valueOf(eingabe.next()); ergebnis = (eingabe1*eingabe1)*Math.PI; System.out.println("The area of a circle having a radius of " + f.format(eingabe1) + " cm is: " + g.format(ergebnis) + " qcm"); }